Method and system for non-destructive distribution profiling of an element in a film

ABSTRACT

A method to determine a distribution profile of an element in a film. The method comprises exciting an electron energy of an element deposited in a first film, obtaining a first spectrum associating with the electron energy, and removing a background spectrum from the first spectrum. Removing the background value generates a processed spectrum. The method further includes matching the processed spectrum to a simulated spectrum with a known simulated distribution profile for the element in a film comparable to the first film. A distribution profile is obtained for the element in the first film based on the matching of the processed spectrum to a simulated spectrum selected from the set of simulated spectra.

RELATED APPLICATION

This application is related to and claims the benefit of and priority toU.S. Provisional Patent application Ser. No. 60/698,367 filed Jul. 11,2005, with Attorney Docket 007029.P029Z, which is hereby incorporated byreference in its entirety.

FIELD

Embodiments of the present invention pertain to a method and system forextracting depth distribution information of an element or elementsdeposited in a thin film or an ultra-thin film.

BACKGROUND

Analysis of the composition of a sample is necessary in the manufactureof many different types of devices. The composition of a sample is theconcentration of an element and/or chemical species in a thin film. Anexample of a sample that may require composition analysis is a gateoxide film formed in a semiconductor integrated circuit device. As thedensity of an integrated circuit chip in a semiconductor deviceincreases and the dimensions of the device continue to be reduced,sample analysis becomes harder and more complex.

For example, recent developments in the fabrication of semiconductordevices may employ shallow implant and/or other ultra-thin structures.In one particular example, gate oxide layers are becoming very thinfilms, typically less than about 10 nanometers in thickness. Such thinfilms are difficult to characterize. Such structures will requirecharacterization techniques that have improved sensitivity overconventional characterization techniques. Further, such techniques mayalso require the characterization to be performed with ample speed.

Various techniques have been used for surface analysis of trace and/ormajor components in such materials. For example, several of such methodsinclude secondary ion mass spectrometry (SIMS), x-ray photoelectronspectrometry (XPS) (also known as electron spectroscopy for chemicalanalysis (ESCA)), and Auger electron spectrometry (AES). Such techniquesare sensitive to the near-surface region of a material. However, thesetechniques do not permit measurement of material properties as afunction of depth beneath the surface through depth profiling.

In a typical depth profiling process, for example, continuous orperiodic ion beam sputtering removes material from the surface of asample to expose progressively deeper material at one or more variousdepths of the sample for further measurement and/or analysis. Generallyknown sputter rates may be used to determine the depth at which thesurface measurements are completed. As such, a characterization of thesample as a function of depth beneath the surface can be attained usingSIMS, XPS, or AES.

Many of the techniques described above for characterizing thin films areinvasive techniques, e.g., they involve destruction of at least one ormore portions of the sample. Such techniques, e.g., those that useremoval of material during depth profiling, are sufficient in manycircumstances, e.g., research and development, product testing, etc.,but do not provide for the ability to quickly analyze a thin film suchas is necessary in production processes. For example, in such productionprocesses, a thin film being formed typically needs to be analyzed sothat such information can be used for production control, product test,etc., without loss of product due to invasive characterization of suchfilms.

SUMMARY

Embodiments of the present invention relate to a method and a system forexamining microelectronic structures and specifically to a system and anon-destructive method for detecting the depth distribution of one ormore elements in a film using photoelectron spectroscopy.

Embodiments of the present invention also relate to a method and asystem for examining microelectronic structures and specifically to asystem and a non-destructive method for detecting the centroid of thedistribution of one or more elements in a film using photoelectronspectroscopy.

Embodiments of the present invention also relate to a method to designand/or monitor an engineering and/or fabrication process of one of moreelements in a film. Accurate materials manufacturing control can be doneonly when one or more reliable control parameters are available. Thedetermined centroid of the depth distribution (the depth of the centerof mass distribution of the element under consideration in a film/layer)and the ratio between the centroid and the thickness of a layer, can beused as control parameters in a process design, monitor and control.Such parameters are accurate predictors of the electrical properties ofthe engineered/fabricated device on the particular film. For example,for SiON films, in transistor design the determined centroid of theelement depth distribution and the ratio between the centroid andthickness of the films correlate to drive current, charge mobility andthreshold voltage. The determined centroid can also be used to compute acorrection to the dose of an element in a film that can be applied tothe standard dose measured by traditional photoelectron spectroscopy(e.g., XPS measurement) thus, improving the correlation between dose andelectrical parameters. The dose of a given element can be used topredict EOT (Equivalent Oxide Thickness), leakage current, therefore canalso be used in process control. The accuracy of XPS measurement of thedose can be significantly improved using the centroid information.

In a photoelectron spectroscopy measurement system, electrons areionized from a characteristic element by some means of excitation (forexample by illuminating a sample with a photon flux of energy higherthan the ionization energy for a given element orbital). The number ofionized electrons that leave the surface of the sample within a certainsolid angle are counted in a detector as a function of their energy

Electrons ionized from a given element orbital (electron species) willbe detected over a broad energy range because they will lose energythrough inelastic scattering interaction with the ionized atoms fromwhere they are emitted (intrinsic losses), with atoms in the lattice ofthe films (bulk scattering) and with the atoms at the interface (surfacescattering).

Models of electron transports that account for bulk and surfacescattering have been developed and published by several authors, and soare techniques to simulate the energy spectrum of photoelectrons emittedby a given species once their initial energy distribution (intrinsicspectrum) is known.

A photoelectron energy spectrum contains the superposition of spectra ofseveral electronic species emitted by different element with differentdepth distributions. The amount of energy lost by each species dependson how long the photoelectrons travels within the film—i.e. depends onthe depth of origin of the photoelectrons. In theory, given the depthdistribution of a single element in a film, the intrinsic spectrum (theenergy distribution of photoelectrons leaving the atom) can be derivedfrom the energy spectra of the photoelectrons emitted by each singlespecies of such element, by subtracting the bulk and surface inelasticscattering contribution from the measured energy spectra. In practice, ameasured spectrum contains the superposition of several elements andtheir several species and no mathematical method is available to readilyextract the intrinsic spectrum of multiple species when they aresuperimposed in the spectrum.

In one general aspect of the present invention, several methods toanalyze spectra and separate the spectral contribution of one or morespecies (preprocessed spectrum) are provided.

An embodiment of the present invention pertain to a method to isolatethe signal emitted by a first species (signal spectrum) from the signalsemitted by different species (background spectra) whose initial emissionkinetic energy is larger than the kinetic energy of the first species.The photoelectrons emitted by the different species will lose energythrough inelastic scattering and will be detected in the same energyrange as the photoelectrons from the first species. So the detectedspectrum is the sum of the background spectrum and the signal spectrum.

An embodiment of the present invention pertains to subtracting abackground spectrum from a measured spectrum by obtaining an independentmeasurement of the background spectrum, e.g., by collecting aphotoelectron spectrum on a sample (background sample) with the samebulk/surface property of the sample of interest that does not containthe element to be analyzed.

In many instances, such a background sample is not readily available. Anembodiment of the present invention pertains to a method of collectingand storing several background spectra on films that are differentbecause of one or more defining parameters (thickness, density . . . ).The background spectra are used to reconstruct an appropriate backgroundfor a particular sample by interpolating between these spectra in theparameter space that describe the difference between each of thebackground samples (difference in thickness, density . . . ).

Another embodiment of the present invention pertains to a method toreconstruct an appropriate background spectrum from prime principlesusing an electron transport theory. Most of the background elements ofwhich the bulk film is composed are of known or uniform depthdistribution. Therefore, when an intrinsic spectrum for each of thespecies at high emission kinetic energy is known, the full backgroundspectra can be reconstructed, normalized and subtracted to isolate thespectra of the photoelectrons emitted by the species with unknown depthdistribution.

An embodiment of the present invention pertain to a method for obtainingintrinsic spectra for multiple species using a set of reference wafersof known depth distribution. The method comprises exciting and acquiringa photo-electron energy signal from a film whose elemental depthdistribution is known, and obtaining an intensity spectrum. Theintensity spectrum is subdivided in kinetic energy regions (subregions),each one containing the emission energy peak/peaks of one or morespecies of the same element (same depth distribution) and each oneextending to at least the first 20-40 eV below the emission energy. Theintrinsic spectrum of each species is determined for each of the energysubregion. The intrinsic spectral determination begins with thesubregion at the highest kinetic energy (initial region). The initialregion contains radiation emitted by the species whose ionization energyis smaller. The energy spectrum of this species does not requiresubtraction of a background prior to its analysis (except for strayradiation that can be approximated as a fixed/linear offset). Thus, theintrinsic function for this species in the energy subrange can beextracted using any available deconvolution technique (Fourier transformbased inversion, regression methods . . . ). The intrinsic function isthen extrapolated to the full energy region for this species. Theextrapolation can be done choosing any arbitrary functional form, forinstance a simple polynomial fit or an exponential, as long as itsatisfy the physics requirements of falling to zero within a reasonablerange and generating a background spectra for the analysis of the otherspecies in the film that is consistent with the observation. Theintrinsic function of the highest kinetic energy species is then used toregenerate a simulated spectrum in the full energy range. Theregenerated spectrum is the background spectrum to the second highestemission kinetic energy species, and therefore will be subtracted fromthe measured spectrum to obtain a processed spectrum. In this processedspectrum, the species that is emitted in the second highest kineticenergy range can be analyzed in the exact same way as done for the firstspecies.

Embodiments of the present invention also pertain a method ofdetermining a distribution profile for an element in a film. The methodcomprises exciting and acquiring a photo-electron energy signal from afirst film, obtaining a first intensity spectrum associated with theelectron energy, and removing a background spectrum from the firstspectrum. The background spectrum can be obtained with any of themethods previously as well as herein described. Removing the backgroundspectrum generates a processed spectrum. The method further includeschoosing a parameterization for the depth distribution that capturesonly the available information. The meaning of available information canbe explained as followed. A depth distribution can be uniquelyidentified by its distribution moments (centroid=1^(st) moment,width=2^(nd) moment, asymmetry=3^(rd) moment and so on). Theinelastically scattered signal can be expressed as the sum of terms ofdecreasing amplitude as a function of the ratio between depth andinelastic mean free path each multiplied by the distribution moments.Detection of a given order of the distribution moments with a desiredrepeatability performance depends on the S/N ratio. The higher the orderof the moments to be detected the better signal-to-noise (S/N) will berequired. For example, for a given element in a first film the S/N levelmight be such that only the first moment (centroid) can be detected withthe desired repeatability while for an element in a second film the S/Nis such that multiple orders of the depth distribution can be detected.In one embodiment, a parameterization of the depth distribution isselected for the first film with a fixed shape distribution and with avariable centroid. The difference in the signal between the real depthdistribution and the simplified one will be buried in the noisetherefore will not contribute to the signal. In an embodiment of thisinvention, a parameterization of the depth distribution will consist ofa set of appropriately chosen parameterization. In one embodiment, auniform distribution (homogeneous film) is identified with the width ofa step function, and a peak like distribution is identified by the depthof its maximum and the width of the curve. In one embodiment, aGaussian-shaped distribution is used to detect the first two moments,width and centroid. Once the parameterization of the depth distributionis chosen, the difference between the processed spectrum and a simulatedspectrum as a function of the parameters is minimized to find the depthdistribution. In one embodiment, a simulated spectrum is obtained usingelectron transport models and an assumed depth distribution. Aconventional minimization algorithm is then used to perform theminimization, such as a Simplex algorithm, a Levenberg Marquardtalgorithm or a search for a best match in a database of pre-computedenergy spectra. The result of the minimization yields the informationabout the distribution profile for the element in the film.

Embodiments of the present invention also pertain a method ofdetermining a distribution profile for an element in a film. The methodcomprises exciting and acquiring a photo-electron energy signal from afirst film, obtaining a first intensity spectrum associated with theelectron energy, and removing a background spectrum from the firstspectrum. The background spectrum can be obtained with any of themethods previously as well as herein described. Removing the backgroundspectrum generates a processed spectrum. The method further includesparameterizing the depth distribution of the element under considerationand minimizing the difference between an independently measuredintrinsic spectrum for that species and the intrinsic spectrum derivedfrom the processed spectrum as a function of depth distributionsparameters. A conventional minimization algorithm can be used to performthe minimization such as a Simplex algorithm, a Levenberg Marquardtalgorithm or a search for a best match in a database of pre-computedenergy spectra. The result of the minimization yields the distributionprofile for the element in the first film.

In one embodiment, from the distribution profile, a centroid for theelement is determined. The centroid of an element in a film is the depthof the center of mass of the concentration of the element in the film.Most of the physical properties of the film can be determined by theknowledge of the centroid. In one aspect of the present invention, thecentroid value is used to predict the electrical properties of a devicefabricated on or in the film and/or control or monitor the fabricationprocess of the device.

Embodiments of the present invention also provide a method to simulate,in real time, a modeled spectrum with a known distribution profile.Statistical coefficients (known in electron transport theory as thePartial Intensities—PI coefficients) characteristic of the depthdistribution of a given species and the scattering process (elastic andinelastic) can be pre-computed, for example, using a Monte Carlo orother suitable methods. The PI coefficients are pre-computed for asparse set of depth distributions and stored in a PI coefficientsdatabase. Such set of PI coefficients can be organized in the databaseas a function of parameters defining the associated depth distributions.Several interpolation techniques can be used to interpolate the PI, e.g.N-dimensional linear or higher order polynomial interpolation. During areal time simulation of the spectrum associated to an arbitrary depthdistribution the appropriate PI coefficients are found by interpolatingthe pre-computed PI coefficients in the space of parameters describingthe depth distribution. The interpolated PI coefficients are then usedto reconstruct the spectrum which is used as a simulated spectrum (forexample a background spectrum or a signal spectrum pertaining to theelement of interest) or is used to reconstruct the scatteringcontribution that can be subtracted from a processed spectrum (aspreviously discussed) to obtain an intrinsic spectrum. The same type ofinterpolation scheme can be done if the full spectra associated to thesparse set of depth distribution is stored, but that would require amuch larger storage memory for the database.

In another aspect of the present invention, a method to extract thecentroid of an element depth distribution directly from the attenuationof multiple species of the same element is described.

In another aspect of the present invention, a method of determining acentroid of a distribution profile for an element in a sample film isprovided. The method comprises exciting and acquiring a photo-electronenergy signals from two species of the same element in the film andobtaining an intensity ratio for the photoelectrons signals (e.g., fornitrogen in SiON, an N1s photoelectron and an NKLL Auger photoelectronare acquired). A set of ratios of signal intensities is obtained for aset of samples of known centroids of a particular element (e.g.,nitrogen) to generate a calibration function. The measured ratio ofsignal intensities of the sample film is correlated to the calibrationfunction to determine the centroid of the distribution profile for theelement. The centroid of the element in the film is the depth of thecenter of mass of the concentration of the element in the film. Most ofthe physical properties of the film can be determined by using thecentroid value. In one aspect of the present invention, the centroidvalue is used to predict the electrical properties of a devicefabricated in or on the film and/or control/monitor the fabricationprocess of the device.

Depth distribution information can also be extracted from theattenuation of the intensity of the unscattered electrons collected atdifferent emission angles, for instance using ARXPS. The methoddescribed in literature is based on the assumption that unscatteredelectrons emitted at depth z and collected at emission angle θ

$^{\frac{z}{{\lambda \cos}\; \theta}}.$

have been attenuated by a factor A coarse depth distribution can befound by optimizing the difference between the attenuation measured as afunction of theta and the attenuation expected assuming a depthdistribution for the element under consideration, i.e. minimizingMeasuredAttenuation

$(\theta) - {\int{{{{zN}(z)}}^{\frac{z}{{\lambda \cos}\; \theta}}\mspace{11mu} {as}\mspace{14mu} a}}$

function of the element depth distribution N(z). Such measurement isimpacted by systematic errors arising from neglecting the angulardependence of the attenuation that all electrons suffers crossing thematerial/vacuum interface and the systematic error introduce byneglecting the angular straggling due to elastic scattering.

In one embodiment of this invention we claim a method to collectelectron spectra at various collection angles, preprocess the data byeliminating surface scattering contribution from the spectra using adeconvolution technique (one or more techniques can be used for examplefast Fourier transform deconvolution or Dr. Werner deconvolutiontheorem) to subtract the systematic error due to interface crossingprior to minimization. For samples engineered in such a way that thedepth distribution of the element under consideration extend to thetypical elastic scattering length the preprocessed signals can beanalyzed including the effect of elastic scattering to improve theaccuracy of the result. That is done by including elastic scatteringeffects in modeling the attenuation. The difference between the measuredattenuation as a function of angle and the attenuation predicted for agiven depth distribution by a Monte Carlo simulation that includeselastic scattering effects is minimized as a function of assumed depthdistribution. The impact on minimization speed of the Monte Carlosimulation can be mitigated by parameterizing the depth distribution aspreviously described, pre-computing the attenuation as a function ofangles for a sparse set of parameters and store it in the database. Theattenuation values needed for a specific depth distribution can beobtained by database interpolation.

In several embodiments of the present invention, we have describedembodiments of deriving signals by interpolations from a set ofpre-measured or pre-computed spectra as a technique to obtain anexpected signal without specifically measuring the expected signal orgenerating it. A signal generated during minimization process is solelyused to compute a figure of merit. A figure of merit is usually definedas a single number that quantify the difference between the measured andsimulated signal, for instance an Mean Square Error is defined as

${FigureOfMerit} = {\sum\limits_{Energy}^{\;}\left( {{{Measured}({Energy})} - {{Simulation}({Energy})}} \right)^{2}}$

An alternative way to solve a minimization problem is to firstpre-compute the figure of merit associated with all pre-computedsimulated spectra contained in a sparse database (Sparse Figure ofMerit). Each pre-computed value of the sparse figure of merit isassociated with a set of parameters uniquely defining a depthdistribution. The sparse figure of merit can be finely interpolated toproduce a figure of merit surface. The minimum of that surface in thedepth distribution parameter space can easily be found by one of themany minimum search methods, i.e., root finding methods or steepestdescent methods. The minimum of that surface defines the depthdistribution profile for the element of interest.

Other embodiments are also described. Other features and advantages ofthe present invention will become apparent from the following detaileddescription, taken in conjunction with the accompanying drawings, whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF TEE DRAWINGS

The embodiments of the present invention are illustrated by way ofexample and not by way of limitation in the figures of the accompanyingdrawings in which like references indicate similar elements. Theinvention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. It should be noted that references to “an”or “one” embodiment of the invention in this disclosure are notnecessarily to the same embodiment, and they mean at least one. In thedrawings:

FIGS. 1-3 illustrate exemplary analysis systems that can be used forcertain embodiments of the present invention;

FIG. 4 illustrates an exemplary process of analyzing an distributionprofile of an element in a film;

FIG. 5 illustrates an exemplary method of determining a distributionprofile of an element in a sample film;

FIG. 6 illustrates another exemplary method of determining adistribution profile of an element in a sample film;

FIG. 7 illustrates an exemplary method of determining a backgroundspectrum to be used for a sample film;

FIGS. 8-9 illustrate pictorially a background subtraction method;

FIG. 10 illustrates exemplary possible distribution profiles;

FIGS. 11-12 illustrate an exemplary method of determining a centroidvalue for an element in a film using intensities' ratio;

FIG. 13 illustrates a calibration curve that can be used in a method ofdetermining a centroid value of a distribution profile of an element ina sample film using signal intensity ratios;

FIG. 14 illustrates an exemplary spectrum having multiple electronsignals representing multiple elements in a film;

FIGS. 15-16 illustrate exemplary methods of simulating one or morespectrum using the simulated spectrums for background subtraction andmethods of analyzing multiple elements in a film; and

FIGS. 17-18 illustrate exemplary processes according to one or moreembodiments of the present invention.

DETAILED DESCRIPTION

Exemplary embodiments are described with reference to specificconfigurations and techniques. Those of ordinary skill in the art willappreciate the various changes and modifications to be made whileremaining within the scope of the appended claims. Additionally, wellknown elements, devices, components, circuits, process steps and thelike are not set forth in detail.

Embodiments of the present invention pertain to a method and system forextracting depth distribution information and/or a centroid value of anelement or elements deposited in a thin film or an ultra-thin film. Sucha film would have a film thickness below 20 nm or most often, below 10nm, and even below 2 nm. It is anticipated that the embodiments of thepresent invention are similarly applicable to analysis of films withthickness about 20 nm or greater. In one general aspect of the presentinvention, a depth distribution profile for an element in a film isdetermined. First, one or more measured energy spectra (or a measuredenergy signal) collected at one or more angles relative to the normaldirection to the sample surface are collected. Second the background ofthe measured energy spectra that is obtained for the element in the filmis subtracted from the measured energy spectrum. The backgroundinformation to be used is obtained by an interpolation method using aselected set of background spectra. In one embodiment, the measuredenergy spectrum is obtained using a photoelectron spectroscopy systemsuch as x-ray photoelectron spectrometry (XPS). The measured energyspectrum with the background removed is referred to as a processedenergy spectrum for the element. Next, the processed energy spectrum ismatched against a modeled or simulated energy spectrum or energy signal.In one embodiment, an optimization and minimization method is performedto match the processed spectrum to a simulated spectrum as a function ofselected parameters that define the distribution profile for theelement. When the difference between the processed spectrum and aparticular simulated spectrum is the smallest, the parameters associatedwith the particular simulated spectrum provide the distribution profilefor the element in the film.

In another general aspect of the present invention, a centroid value forthe elemental depth distribution is determined by utilizing a ratio ofsignal intensities that originate from emission signals of differentkinetic energies but of the same element (e.g., for nitrogen in SiON, anN1s photoelectron and an NKLL Auger photoelectron). Different emissionlines due to the same element (different species) will have differentkinetic energies. Having different kinetic energies, the electrons fromeach of the species will experience different attenuation when theytraverse a film layer. The higher energy electrons will experience lessattenuation when passing through material than lower energy electrons.For instance, taking nitrogen as an exemplary element, the electron fromthe N1s species of nitrogen has a higher electron energy than theelectron form the NKLL species. The centroid of the nitrogendistribution in the SiON film, can be determined using the ratio ofN1s/NKLL intensities. The intensity ratio is governed by the differentattenuation length λ(N1s) and λ(NKLL) at the different emission energyfor the N1s and NKLL species, respectively. Given that the signalsoriginate from the same element and the same in-depth distribution, thesignal ratio correlates with the centroid of the element in the film. Aset of ratios of signal intensities is provided for a set of knowncentroid for a particular element (e.g., nitrogen) to generate acalibration function. The measured ratio of signal intensifies of thesample film is correlated to the calibration function to determine thecentroid of the distribution profile for the element.

Throughout this discussion, the term “element” may be used to refer to achemical composition of a specific layer or substrate. The term“element” may also be used to refer to an elemental species deposited ina specific layer or substrate. For example, a hafnium oxide layerincludes an element of hafnium and oxygen or a silicon oxynitride layerincludes an element of silicon, nitrogen, and oxygen. An “electronspecies” or a “photoelectron species” refer to an electron having acharacteristic energy. A single element may emit several differentelectron species. For example, a silicon substrate may emit twodifferent characteristic electrons having different kinetic energies.One electron may be emitted from the 2p orbital of the silicon atom,while the other electron may be emitted from the 2s shell of the siliconatom. In another example, a silicon oxynitride layer may emit twodifferent characteristic electrons for the nitrogen element havingdifferent kinetic energies. One electron may be emitted from the N1sorbital of the nitrogen atom, while the other electron may be emittedfrom the NKLL (Auger region) of the nitrogen atom. An electron signalhereinafter refers to a stream of electrons belonging to a specificelectron species. For example, a “nitrogen N1s electron signal”comprises electrons emitted by the nitrogen atom from the N1s region.For example, a “nitrogen NKLL electron signal” comprises electronsemitted by the nitrogen atom from the Auger region or NKLL region. Manyof the embodiments discussed below refer to photoelectrons or electronsthat are emitted when a layer is bombarded with photons. Each elementalspecies may emit one or more photoelectron species, which may comprise aphotoelectron signal. An electron energy signal may have a single valueor may be indicated in a spectral line.

As used herein, characterization or analysis refers to the determinationof one or more characteristics of the sample being analyzed. Forexample, characterization may refer to a distribution profiling or depthprofiling of a sample or portion thereof, a determination ofconcentration of components in a sample, a distribution of suchcomponents, or a determination of one or more other physical or chemicalcharacteristics of the sample, e.g., thickness of regions, bondingstates in the regions, elemental and chemical composition in theregions. The present invention is particularly beneficial in thedetermination of the concentration or dose of components (e.g., elementsand/or chemical species) versus depth in a sample film.

Throughout the discussion, the term “distribution profile” may be usedgenerally to refer to deposition depth, deposition profile, depositionwidth, and centroid value of an element deposited in a film. A “centroidvalue” or a “centroid” of a distribution is defined as

${centroid} = \frac{\int_{0}^{\infty}{{N(z)}z\ {z}}}{\int_{0}^{\infty}{{N(z)}\ {z}}}$

where N(z) is the concentration depth distribution and z is the depth.The centroid is thus the average depth of an element in a film, e.g.,the nitrogen in an SiON film, or the depth of the center of mass of theelement. A “dopant” generally refers to an element (e.g., nitrogen)being deposited in a film. A “dose” generally refers to a count orconcentration of an element or a dopant being deposited in a film.

FIGS. 1.3 illustrate exemplary analysis systems that can be used withone or more embodiments of the present invention. FIG. 1 generally showsone embodiment of an illustrative analysis system 1600 operable for usein characterizing a sample 1602. The analysis system 1600 includes aprocessing system 1604 (e.g., a computer apparatus) operable undercontrol of one or more programs 1606 to carry out one or more variousdepth profiling, centroid determination, and/or characterizationprocesses in according to embodiments of the present invention.

The sample 1602 having a sample surface 1608 may be formed of any one ormore components and/or which may be formed on a substrate 1610. The termcomponent is defined herein as one or more elements and/or chemicalspecies. For example, such components may include elements and/orchemical species composing materials used in semiconductor fabrication,magnetic storage media, or any of the other various applicationsdescribed above. In other words, for example, in the context ofsemiconductor fabrication the sample may include layers formed ofoxygen, silicon, carbon, fluorine, silicon dioxide, nitrogen, etc.

The processing system 1604 includes a computing system operable toexecute the computer program or software 1606 to provide for thecharacterization of samples according to certain embodiments of thepresent invention. Although the processing system 1604 may beimplemented using the program 1606, executable using a processorapparatus, other specialized hardware may also be used to providecertain functionality required to provide a user with characterizationof a sample. As such, the term processing system 1604 as describedherein includes any specialized hardware or computer in addition toprocessor apparatus capable of executing various software routines.

The processing system 1604 may be, for example, any fixed or mobilecomputer system, e.g., a personal computer, and/or any other specializedcomputing unit provided as a functional part of or as a supplement to ananalysis instrument used according to the present invention. The exactconfiguration of the computer system is not limiting and most any devicecapable of providing suitable computing capabilities and/or controlcapabilities may be used according to the present invention. Further,various peripheral devices, such as a computer display, a mouse, akeyboard, a printer, etc., are contemplated to be used in combinationwith a processor in the processing system 1604. For example, a computerdisplay printer may be used to display depth profile information, e.g.,depth profile curves showing concentration of components (e.g., elementsand/or chemical species) at depths of the sample, distributions ofcomponents across a sample at a particular depth, spectra of thecomponents, etc.

The analysis system 1600 according to the present invention includes anx-ray source 1612 operable to irradiate the sample 1602 with x-rays 1614resulting in the escape of photoelectrons therefrom. As shown in FIG. 1,the x-rays 1614 penetrate deep into the sample surface 1602, excitingphotoelectrons 1616 and 1618 to escape from the sample 1602.

The analysis system 1600 also includes an analyzer 1620 operable todetect photoelectrons 1616 and 1618 escaping from the sample. Theanalyzer 1620 is used to detect photoelectrons for generation of asignal representative thereof to be used in the distribution profileanalysis for the sample 1602. Signals from the analyzer corresponding tointensity of detected photoelectrons are provided to the computerapparatus, which operates on the signals to provide photoelectron energyinformation, and thereby information on components that are present inthe sample surface at the depth being analyzed. The analyzer system 1600can be replaced by or combined to a conventional XPS system, anUltraviolet Photoelectron Spectroscopy (UPS) system, an AugerSpectroscopy system, etc.

FIG. 2 shows in more detail one illustrative embodiment of portions ofan analysis system 71 operable for carrying out the Characterizationaccording to certain embodiments of the present invention. The analysisinstrument 71 shown in FIG. 2 for analysis of a sample 2 (which can bethe sample 1602 previously shown or other samples) provides a moredetailed illustrative embodiment of the x-ray source 9, the analyzer 7,and the computer apparatus 13 shown generally in FIG. 1. FIG. 2 haspreviously been described in U.S. Pat. No. 5,315,113 to Larson et al.,issued 24 May 1994, and entitled “Scanning and High Resolution X-rayPhotoelectron Spectroscopy and Imaging.” The detailed diagram of FIG. 2is but one illustrative embodiment of an x-ray source and an analyzerthat may be used according to the present invention and is not to beconstrued as limiting the present invention to any particular componentsshown therein.

The instrument 71 of FIG. 2 includes an electron gun 16 having anappropriate electron lens system 18 for focusing the electron beam 20onto the surface 22 of a target anode 24. The electron gun 16 may be aconventional type, modified to optimize for higher power and larger beamsize. The gun beam 20 is focused to a selected spot on the anode surface22. The spot is preferably as small as practical, e.g., down to about 4microns. The focusing of the beam 20 onto the spot of the anode surfaceresults in the generation of x-rays 27 from the anode 24 and,particular, from the selected anode spot. The electron gun may be anysuitable gun such as one operable at 20 kV over 1 watt to 60 watts witha selectable beam size of 4 microns to 50 microns, as described in U.S.Pat. No. 5,315,113.

The target anode 24 may be formed of any metal such as aluminum thatprovides a desired x-ray emission energy band. For example, the band isgenerally substantially a line of small energy width. Preferably, thetarget anode is at or near ground potential, and the gun cathode isoperated at a negative voltage, for example, −20 kV, with respect to theanode to effect generation of x-rays including the desired band ofx-rays of predetermined energy. In one preferred embodiment, theselected energy band is the aluminum K-alpha line at 1.4866 keV.

Deflection plates 28 selectively direct or aim the electron beam 20 fromthe electron gun 16 to the spot on the anode 24 which is selected out ofan array of such spots on the anode surface 22. Voltages from adeflection plate control 30, controlled by a processor 76 via line 80,are applied to the deflector plates, which are arranged in both x and yaxes, to establish the amount of deflection of the beam, and thereby theselected position of the spot. The spot may be held stationary.Alternatively, the control 30 may provide rastering of the focusedelectron beam 20 across the flat surface of the anode, e.g., over thearray of anode spots across the anode surface, and the x-rays 27 areemitted sequentially from successive anode spots. For example, rasterspeed may be 100 Hz in the dispersive direction and 10 kHz in thenon-dispersive direction.

A Bragg crystal monochromator 34, advantageously single-crystal quartz,is disposed to receive a portion of the x-rays 27 from the anode 24. Themonochromator has a crystallographic orientation and a concaveconfiguration 35 to select and focus a beam of x-rays 36 in the desiredenergy band, e.g., the K-alpha line, as an x-ray spot on the samplesurface 12 to be analyzed. The x-ray spot is an image of the anode spoton the sample surface 12. Alternatively, rastering of the x-ray spot maybe used to cover a desired area of the sample surface. The sample 2rests on a stage 40 advantageously having orthogonal micrometerpositioners 41 for manual or motorized positioning with respect to asupport 44 in the instrument. The sample 2 may be moved to providecoverage over an even larger surface area.

Although a Bragg crystal monochromator is preferred, other focusingapparatus may be suitable. Such focusing apparatus may include grazingincidence mirrors, Fresnel zone plates, and synthetic multilayer devicesof alternating high and low density material (e.g., tungsten andcarbon). In each case, the reflector is curved to focus the diffractedx-rays onto the specimen.

A suitable arrangement of components for the analysis instrument 71 isbased on the conventional Rowland circle 46. In this arrangement, theanode surface 22, the crystal 34, and the sample surface 12 aresubstantially on the circle, for example, as taught in U.S. Pat. No.3,772,522, to Hammond et al., issued 13 Nov. 1973 and entitled “CrystalMonochromator and Method of Fabricating a Diffraction Crystal EmployedTherein.”

The x-rays 36 cause photoelectrons 52 to be emitted from the selectedactive pixel area of the sample. The electron energies generally includea low energy peak in the range of up to 10 eV, usually about 2 to 5 eV,plus higher kinetic energy peaks or lines characteristic of chemicalspecies (e.g., chemical elements and/or their electron bondings) in theselected pixel area. In the case of rastering, the characteristicphotoelectrons vary with any varying chemistry across the array of pixelareas, and the low energy electrons (commonly known as “secondaryelectrons”) vary with topography, as well. Detection and/or analysis ofthe photoelectrons are used to provide information regarding the samplesurface at a selected pixel area or across the rastered array of areasof the sample surface. There also may be Auger electrons, which, for thepresent purpose, are included in the term “photoelectrons” as they arecaused by the x-rays.

In one embodiment of the invention, an electron energy analyzer 54receives a portion of the photoelectrons 52. The analyzer may be a knownor desired type, generally either magnetic or electrostatic, whichdeflects the photoelectrons in a predetermined path 68 according toelectron energy and then to a detector 70. A selected control, generallyan electrical signal (current or voltage), is applied to the deflectorto establish the amount of deflection and so is representative ofselected energy of photoelectrons deflected in the predetermined path.In a magnetic analyzer such as a magnetic prism, a current signalthrough the magnet coils is appropriately selected, and in anelectrostatic analyzer a deflecting voltage signal is selected.

One useful type of electrostatic energy analyzer is a cylindrical typedescribed in U.S. Pat. No. 4,048,498, to Gerlach et al., issued 13 Sep.1977 and entitled “Scanning Auger Microprobe with Variable AxialAperture.” In a preferable alternative, as shown in FIG. 4, the analyzer54 is a hemispherical type as described in U.S. Pat. No. 3,766,381, toWatson, issued 16 Oct. 1973 and entitled “Apparatus and Method ofCharge-Particle Spectroscopy for Chemical Analysis of a Sample.” Theanalyzer also includes a lens system 56 such as an electrostatic lensfor the input to the analyzer. The lens system 56 has a central axis 57therethrough along which system 56 lies. The lens system 56 may combineobjective and retarding functions to collect photoelectrons emitted fromthe effective pixel area and direct them into the analyzer in thedesired kinetic energy range.

The electrostatic lens system 56 may be conventional, for example, a PHIOmnifocus IV™ lens available from Physical Electronics Inc. The lensshould include pairs of orthogonal deflection plates with appliedvoltages from a source 62. The voltages are selected, varied; oroscillated via the processor 76 in cooperative synchronization withpositioning or rastering of the primary electron beam 20, under controlof the processor, to centralize off-axis photoelectrons so that asubstantial portion of the electrons reach the slit 84 and enter intothe analyzer 54.

An alternative for the objective lens function is a magnetic lens,advantageously of a type variously known as an immersion lens, a singlepole piece lens or a snorkel lens as described in U.S. Pat. No.4,810,880, to Gerlach; issued 7 Mar. 1989 and entitled “Direct ImagingMonochromatic Electron Microscope.” This objective lens is situatedbelow the sample so that the magnetic field of the lens collects asubstantial portion of the emitted photoelectrons from the samplesurface. To achieve this, the sample is placed proximate the immersionlens, the sample being interposed between the immersion lens and aseparate electrostatic lens which form the lens system. More generally,the sample is located between the immersion lens and the analyzer. Themagnetic lens may have a collection zone of electrons emitting from aportion of specimen surface being rastered.

Yet further, preferably, the lens system is an electrostatic lens withtwo spherical grids, similar to the Omega™ lens available from PhysicalElectronics Inc. Such a lens system is used in the PHI Quantum 2000Scanning ESCA Microprobe™ available from Physical Electronics Inc.

With a selected voltage from a voltage source 62 applied via lines 69across the hemispheres 64, 66 of the analyzer, electrons of selectedenergy travel in a narrow range of trajectories 68 so as to exit theanalyzer into the detector 70. The latter may be a conventionalmultichannel detector, for example, having 16 channels for detecting asmall range of electron energies passed by the analyzer in slightlydifferent trajectories. A further lens (not shown) may be placed betweenthe analyzer and the detector, if desired or required for certain typesof detectors.

Signals from the detector 70 corresponding to intensity of photoelectroninput are carried on a line or lines 72 (via an appropriate amplifier,not shown) to an analyzing portion 74 of the processing unit 76, whichcombines control electronics and computer processing. The processingprovides electron energy information and thereby information oncomponents that are present and emitting the photoelectrons from theparticular sample surface area.

The information is stored, displayed on a monitor 78, and/or printed outin the form of images, numbers, and/or graphs. By cooperating thedisplay (which herein includes the processing) with the electron beamdirecting means 28, 30, via line 80 from the processor to the controller30, a mapping of the components in the selected or scanned surface areais effected and displayed. The mapping provides sample surfaceinformation corresponding to the selected pixel area location, or therastered array of pixel areas on the sample surface.

Other portions of the instrument 71, such as the secondary electrondetector 88 and electron gun 98 providing ions 100, are used asdescribed in U.S. Pat. No. 5,315,113.

According to the present invention, and advantageously used in thecharacterization of thin films, the lens system 56 is positioned at ananalyzer angle of a constant angle for improved and faster datacollection. The lens system 56 generally extends along a central axis 57from a photoelectron receiving end 59 to an end coupled to hemisphericalportions of the analyzer 54.

Returning to the analysis system 1600 (FIG. 1), the system is configuredto excite more than one electrons from the same sample 1602 at the samedepth. For example, the system 1600 is configured to excite twodifferent photoelectrons from the sample 1602. In one embodiment, thesample comprises an SiON film and the electrons to be excited from theSiON film associate with the nitrogen element deposited in the SiONfilm. FIG. 1 illustrates that the analysis system 1600 is configured toexcite two different photoelectrons 1616 and 1618. In one embodiment,the photoelectron 1616 is from the N1s region of the film and thephotoelectron 1618 is from the Auger (NKLL) region of the film. TheX-ray source 1612 is illustrated as one unit but may include differentsources that can cause two or more different photoelectrons to be exitedfor the sample 1602.

An analysis system such as the system 1600 is particular useful forcarrying out one or more exemplary embodiments of the present invention.For instance, the system 1600 is used to take measurements for thesamples with known distribution profile that are used to generate acalibration function that is used to analyze an unknown sample. Themeasurements for the calibration function is stored and processed by theprocessing system 1604. When the unknown sample is measured, themeasurements form the unknown sample is also processed by the processingsystem 1604 and interpolated using the calibration function in providedvia the processing system.

FIG. 3 illustrates another exemplary analysis system 1800 that can beused for certain embodiments of the present invention. The analysissystem 1800 is similar to the system 1600. In addition to some of thecomponents similar to the system 1600, the system 1800 includes amodeling system 1830 that can be used to generate signal spectra orsignal values associated with simulated distribution profiles. Similarto the system 1600, the system 1800 includes an X-ray source 1812, ananalyzer 1820, and a processing system 1804. A sample 1802 that includesa film 1808 formed on a substrate 1810 can be analyzed using the system1800.

The system 1800 can be used to carry out one or more exemplaryembodiments of the present invention. Generally, in these methods, asample film is analyzed by having a measured spectrum for a particularelement (e.g., nitrogen) in a sample film (e.g., SiON) processed andcompared to a simulated spectrum to determine the distribution profileof the element in the sample film. In one example, an electron energysignal for nitrogen is obtained by the X-ray source 1812 sending anx-ray into the sample film 1808 and excites the photoelectron 1816. Theanalyzer 1820 detects the photoelectron 1816 and produces a measuredsignal intensity associated with the photoelectron 1816

FIG. 4 illustrates an exemplary analysis method 101 that illustrates ageneral novel approach of determining a depth distribution profile of anelement deposited in a thin sample film. The thin sample film may bedeposited or otherwise formed on a substrate or other film(s). Atoperation 100, an electron energy signal for an element is obtained. Asignal of the element may be represented as an energy spectrum of theelement. The element is deposited in a sample film or in a substrateusing various methods. Often, for an element deposited in a film, thedepth of the element deposition, the distribution of the element, and/orthe distribution profile in the film needs to be analyzed. At box 102, abackground subtraction is performed. At box 104, a processed electronenergy signal is obtained. When the background is subtracted from theelectron energy signal, the signal value obtained is referred to as a“processed electron energy signal.” The background that is removedincludes the energy signal obtained due to the bulk material in thesample film and without the element of interest. Removing the backgroundprovides for the isolation of the energy signal of the element ofinterest only so that analysis can be performed for the elementdeposited in the sample film. To begin the distribution profiledetermination, for the element, at box 106, a simulation distributionprofile is varied (optimization) until the simulated energy signalassociated with the simulation distribution profile matches theprocessed electron energy signal. In one embodiment, the processedelectron energy signal is matched to a simulated energy signal using aminimization and optimization algorithm such as a Simplex algorithm orLevenberg Marquardt algorithm. When the difference between the processedelectron energy signal and a particular simulated energy signal is thesmallest, a matched is obtained. The distribution profile of the elementunder consideration is therefore determined in box 108 as the onesimulated distribution profile that was used to compute the bestmatching simulated spectra to the processed spectrum.

The following discusses in more details the various aspects of theinvention according to the exemplary method 101. FIG. 5 illustrates anexemplary embodiment of a process 201 that analyzes distribution profileof an element deposited in a sample film. In one embodiment, a substrate(such as a wafer) that has the sample film with the element of interestto be analyzed is provided (box 200). An element of interest is nitrogendeposited in a SiON film, in one embodiment. In other embodiments, otherelements deposited in the same film or other films are provided.Numerous elements deposited in various types of sample films can beanalyzed using embodiments of the present invention.

The sample film is placed in an analysis system such as those discussedin reference to FIGS. 1-3. An example of an analysis system includesXPS. Other equipments that can excite electrons from a film and producea readable result from the energy released from the electron or theenergy used to excite the electrons can be used. In one embodiment, thesample film is irradiated with x-rays (using an x-ray source provided inthe analysis system) resulting in the escape of photoelectronstherefrom. The escaped photoelectrons are detected by a detectorprovided in the analysis system. The detected photoelectrons at eachenergy are counted and translated into energy signal (spectra)representative of the film and reported. The energy signal is used forthe analysis of the element. At 204, a measured energy signal orspectrum for the element is obtained.

Next, at 212, the measured energy signal/spectrum is processed. In oneembodiment, in processing the measured energy signal/spectrum, thebackground information 206 of the measured energy signal/spectrum isremoved or subtracted as shown at box 208. After the backgroundinformation is removed, a processed spectrum is obtained at 210.

At 216, the processed spectrum is subjected to optimization to determinethe depth distribution profile of an element in the sample film. At216A, the depth distribution is obtained by minimization of thedifference between the processed energy signal/spectrum and a simulatedspectrum as previously described, e.g., using a minimization algorithm.An intrinsic spectrum is extracted from the processed spectrum andsubjected to a minimization with an intrinsic spectrum with a knowndistribution profile to determine the distribution profile of theelement.

Alternatively, at 216B, the depth distribution is obtained byminimization of the difference between a reference intrinsic spectrumand the intrinsic spectrum derived from the processed energysignal/spectrum as described. The intrinsic spectrum is used to generatea simulated spectrum with a known distribution profile and is minimizedagainst the processed spectrum to determine the distribution profile.

The distribution profile for the element is determined based on theresult of the minimization/optimization process at 218.

The background energy signal/spectrum is the signal/spectrum is emittedby elements of the sample film other than the element of interest, atemission kinetic energy higher than the species under analysis. In oneembodiment, to find the appropriate background energy signal/spectrum, aset of reference background signals/spectra associating with a set ofreference films is obtained. Each reference film is comparable to thesample film in that it is similarly treated and formed except for thelack of the element under consideration. In other words, each referencefilm is like the sample film except that the reference film does nothave the element of interest deposited therein and may have a thicknessdifferent or slightly different from the thickness of the sample film.The same analysis system used to analyze the sample film is used toobtain the background energy signal/spectrums for the reference films.Depending on the thickness of the sample film, a particular backgroundenergy signal/spectrum is either reconstructed from the set byinterpolation or just selected from the set of reference backgroundspectra—if the correct thickness is available.

FIG. 6 illustrates an exemplary embodiment method 300 of a backgroundsubtraction method for a measured energy signal/spectrum obtained for asample film in according to the present invention. At 302, a set ofreference background intensity spectra for various reference films iscollected. The reference films include films having various referencefilm thicknesses. The reference film thicknesses may range from 1-50 nm,which is only an exemplary range of thickness. The chosen reference filmthicknesses may cover a wide selection of thicknesses to a smallerselection of thickness that the sample film or the like is expected tofall within. In one embodiment, the background intensity spectra are thephotoelectron energy signals of the reference films taken using theanalysis system 202 previously mentioned. The intensity spectra takenfor the reference films are spectra taken from the same region of thefilms as the sample film.

At 304, a background table having the reference background intensityspectra, each corresponding to a respective reference film thicknessesis generated. In one embodiment, the background table contains intensityspectra for the reference films as a function of thickness (or depth).The background table may contain other measurable values (thickness,dose . . . ) for the reference films that can be compared to the samplefilm.

At 306, thickness for the sample film is determined. The thickness ofthe sample film can be determined using various methods. An exemplarymethod of determining the thickness of the sample film is disclosed inU.S. patent application Ser. No. 11/118,035 (Attorney Docket 7029.P026),entitled “Determining Layer Thickness Using Photoelectron Spectroscopy,”which is hereby incorporated by reference in its entirety. It is to beanticipated that other methods suitable for film thickness determinationcan be used instead. The determined thickness of the sample film allowsthe film to be compared to the set of reference films that has thebackground energy signals measured as previously described. Thethicknesses for the reference films are also determined using a similarmethod.

At 308, a background intensity spectrum is removed from the sample film.In comparing the measured intensity spectrum of the sample film to thosein the background table, first, determine if the sample film has thesame thickness as one of the reference films in the background table.Then, if the film thickness matches one of the reference films in thebackground table, the background intensity spectrum of that particularreference film (with the matching thickness) is used for the backgroundsubtraction from the sample film. If the film thickness is not alreadyin the background table, a value is interpolated or reconstructed fromthe background table to derive the background intensity spectrum for thesample film. Thus, the background intensity spectrum to be subtractedfrom the sample film can be a reference background intensity spectrumalready in the background table or a value interpolated or reconstructedusing the background table.

It is to be appreciated that although thickness of a reference film anda sample film is one attribute used for the background spectruminterpolation, other suitable or convenient attributes of the films canbe used. Examples of other suitable attributes include concentration,dose, deposition width, deposition condition, film formation, etc.

FIG. 7 pictorially illustrates an exemplary set of spectra for anexemplary set of reference films with their respective energy signals.It is to be understood that the spectra shown here are merely forillustrative purpose and the line shapes and the associated data mayvary depending on the characteristics of the reference films. More orless number of spectra may be included and the exemplary spectraillustrated in this figure may represent only a small number actuallyimplemented for a particular embodiment. In one embodiment, a spectrumis formed from a set of intensity readings or values obtained from aparticular film.

In FIG. 7, the x-axis 402 represents the energy needed to exciteelectrons from the film or the kinetic energy of the electrons and they-axis 404 represents the atom accounts or intensities of the electronsexcited from the reference films and detected. The atom count or theintensities represent the energy signals for each film and are plottedagainst the energy. A sloped spectral line is generated for eachreference film, in one embodiment. In this figure, the energy signalsobtained for six (6) reference films are illustrated. The referencefilms have film thicknesses ranging from 2 Å-30 Å, which are onlyillustrative thicknesses. Other thicknesses may be included. Forexample, the energy spectral line at 2 Å indicates the signals for thereference film having a 2 Å thickness. As the reference film thicknessincreases, the count for the atoms increases. In this case, the slope ofall lines will vary smoothly with thickness, therefore a slope value foran unknown thickness can be obtained by interpolation. For a sample filmwith a thickness X, for example, that falls between certain filmthicknesses, e.g., between 5 Å and 10 Å, an a background spectra for thesample film is reconstructed interpolating the background spectra forthe reference films of thicknesses, e.g., 5 Å and 10 Å. For instance, ifthe sample film has a thickness that falls between 5 Å and 10 Å, theconstructed spectral energy line for the sample film is one that fallsapproximately between the spectral energy lines for the reference filmswith the thicknesses of 5 Å and 10 Å. The reconstructed spectral linefor the sample film with the thickness X can be used for the backgroundsubtraction for the sample film.

FIGS. 8-9 pictorially illustrate an exemplary background subtractionresult for a sample film that contains SiON. In FIG. 8, spectral line602 indicates a measured energy signal spectrum for the sample film thatincludes the background signal as well as the signal of the nitrogenelement. In FIG. 9, the background signal is subtracted as previouslydiscussed. Spectral line 604 represents the energy signals due to thenitrogen alone. As previously discussed, the background signal to besubtracted is determined by comparing the film thickness of the samplefilm to a set of film thicknesses of background reference films. Thebackground signal for the sample film can either be a referencebackground intensity spectrum from the background table or areconstructed background intensity spectrum using an interpolated value.

In one embodiment, the element of interest is nitrogen deposited in asilicon oxynitride (SiON) film. A large portion of the measured energysignals is in the regions of the N1s photoelectron signal and a largeportion of the signals is due to inelastic scattered Si (Si2p and Si2s)photoelectron regions that originate from the SiON film (and from theunderlying substrate). To simulate a set of reference backgroundintensity values, in one embodiment, the N1s region is chosen.Measurements are taken for each reference film at the N1s energy region(in the absence of the nitrogen in the reference film) for eachreference film, which is SiO₂ (since no nitrogen is present in thereference film). The measurements are then curve fitted to predict theshape of the spectral line for each reference film that is Si)₂ for aparticular film thickness. The SiO₂ portion of the spectrum is referredto as a “generic background.” The generic background contribution for anSiON film of a given measured thickness is considered to be identical tothe fitted and extrapolated signal from an SiO₂ film of identicalthickness. The difference between the measured N1s signal region on anSiON film and the corresponding generic background of the same SiO2thickness is considered purely due to un-scattered and inelasticscattered nitrogen from the film. The fitting and prediction of thebackground region may also include other potential surface contaminantlayers such as carbon, etc.

FIG. 10 illustrates some examples of simulated distribution profiles foran element such as nitrogen in SiON. Simulated distribution profiles90A, 90B, 90C, and 90D are provided. These simulated distributionprofiles are provided for illustration purpose only and other profilesare entirely possible. Each of the distribution profiles 90A, 908, 90C,and 90D has an associated energy spectrum. For each of the profiles90A-90D, the distribution profile of the element has a concentrationgoes from 0.1 of the total concentration to 0.9 of the totalconcentration of the element deposited in a film. For each of theprofiles 90A-90D, the depth of the element deposited goes from 1 Å-7 Å.The distribution profiles are stored for each of the profiles 90A-90D.The associated spectral line for each profile is also obtained. If theprocessed spectrum of the sample film (e.g., spectrum A) matches thespectral values of the profile 90A, then it can be expected that thesample film has the element distributed similarly to the profile 90A. Ifthe processed spectrum of the sample film (e.g., spectrum A) matches thespectral values of the profile 90B, then it can be expected that thesample film has the element distributed similarly to the profile 90B.Various distribution profiles can be generated or simulated. Theassociated spectral lines are also determined and stored in a database.A process such as the process 800 can pull a particular distributionprofile form the database and perform the comparison as previouslydescribed. In one embodiment, selecting a particular distributionprofile to compare to the processed spectrum is automated and/orcontinuous until a match is found for the processed spectrum.

FIG. 11 illustrates a characterization process 105 that utilizes a ratioof signal intensities of the same elements. In one embodiment of theprocess 105, electron energy signals are obtained for the element in thethin sample film at 103. A ratio for the measured energy signals of theelement is obtained at 110. At least two different electron species fromthe same element are obtained. The analysis of the sample film involvesthe use of the measured energy signals for the element derived from twoor more different electron species of the same element. In one example,the element is nitrogen and the sample film is a silicon oxynitridefilm. Two different characteristic electrons for the nitrogen elementare emitted and each having different kinetic energy from the other. Inone embodiment, one electron emitted is from the N1s orbital of thenitrogen atom called “N1s energy signal” and the other electron emittedis from the NKLL (Auger region) of the nitrogen atom called “NKLL energysignal.” In one embodiment, the ratio of the two measured energy signalsof the element is indicative of the centroid of the element in the film.At 112, the energy signal ratio is compared against a calibrationfunction to determine the distribution profile for the element in thesample film.

FIG. 12 illustrates an exemplary method 1400 of determining a centroidof an element (e.g., nitrogen) in a film (e.g., SiON). In the method1400, the ratios of two different energy signals for the same elementalspecies are used for this analysis. In one embodiment, the element ofinterest is nitrogen. In the present embodiment, the energy signals fornitrogen at the N1s region and the NKLL (Auger) region are used for theanalysis. Other energy signals can also be used without exceeding thescope of the invention.

At 1402, a wafer is provided. The wafer contains the sample film withthe element to be analyzed. For instance, the wafer is a semiconductorsubstrate with the film SiON formed thereon and the element nitrogen isto be analyzed. The wafer is placed into an analysis system at 1404,e.g., XPS, previously described. At 1406, two energy signals areobtained for the nitrogen in the SiON film. At 1408, the energy signalsare processed. The energy signals are processed to remove any backgroundnoises or other information not pertaining to the signals from theenergies excited from the sample film. At 1410, a signal intensity ratiois computed for the element. The signal intensity for the nitrogen atthe N1s region is expressed as “I(N1s)” and the signal intensity for thenitrogen at the NKLL region is expressed as “I(NKLL).” The ratio for thesignal intensifies is expressed as R(sample). The ratio R(sample) can beexpressed as

R(sample)=I(N1s)/I(NKLL)  (1)

The ratio of the energy signals at the N1s species and the NKLL speciesare useful for centroid determination at least for the followingreasons. The two different energy signals attenuate differently as theytraverse the SiON film. For instance, the attenuation of the energysignal from the N1s species is much less compared to the attenuation ofthe energy signal from the NKLL species. One reason for that is that,originating from a particular depth, the N1s species is emitted athigher kinetic energy compared to the NKLL species and thus, the signalwill attenuate less compared to the energy for the NKLL species, whichhas lower emission energy. The ratio of the energy signals from the N1sand NKLL regions vary as the depth of the nitrogen element varies. Thus,the dependence of the ratio of the signal intensities on the centroidlocation is expressed as:

I(N1s)/I(NKLL)˜e ^(−tc/λ(N1s)) /e ^(−tc/λ(NKLL))  (2)

Where “tc” stands for the centroid value of the element and “λ” standsfor the attenuation length of the element at a particular region. Thus,λ(N1s) stands for the attenuation length of the nitrogen from the N1sspecies and λ(NKLL) stands for the attenuation length of the nitrogenfrom the NKLL species. The attenuation length values are know or can bedetermined.

The ratios thus allows for the extraction of the centroid of the elementin the sample film. It is to be anticipated that the energy signals atother regions for an element can be used. In one embodiment, todetermine the centroid of nitrogen in the SiON film, a calibrationfunction is provided. At 1412, a set of intensity ratios for nitrogen atvarious known centroid values in the SiON film is provided. The ratiosfor the signal intensities for nitrogen deposited with various centroidsare obtained. The ratio of the signal intensities varies according tothe centroid of the depth distribution of the element in the film asillustrated in FIG. 13. At 1414, the signal intensity ratio of theelement is compared to the set of intensity ratios for nitrogen atvarious depths to determine the centroid of nitrogen in the sample film

At 1416, dopant correction and/or determination of nitrogen in thesample film are performed. In the embodiments where XPS or Augerspectroscopy is used, often only about 10 nm of the surface of thesample film is measured. The mean depth of the distribution of theelement in the sample film may introduce some interpretation errors inthe reported atomic concentration or dose of a film constituent. If themean depth of a film dopant (element deposition) is at the surface, noattenuation of the measured signal has to be taken into account. On theother hand, if the mean depth (the centroid) of the element of the samenumber of atoms is, for example, at 3 nm and the electron attenuationlength λ is 3 nm, only a fraction of the emitted electron signal(e^(−tc/λ)) will be detected. In order to improve the accuracy of areported dose or atomic concentration result, the measured signalintensity of the element of interest would have to be corrected by afactor 1/e^((−tc/λ)).

In order to correct the standard XPS dose determination made assuming auniform depth distribution for the element of interest a correctionfactor of

$\frac{^{\frac{T}{2{\lambda {({E{({{Si}\; 2p})}})}}_{{SiO}\; 2}}}}{^{\frac{C}{{\lambda {({E{({N\; 1s})}})}}_{{SiO}\; 2}}}}$

is used. In the correction factor, T=thickness of the film,λ(E(Si2p))_(SiO2)=attenuation length of the Si 2p species in SiO2, andλ(E(N1s))_(SiO2)=attenuation length of the N1s species in SiO2.

FIG. 13 illustrates an exemplary calibration graph 1500. The x-axisrepresents the centroid values and the y-axis represents the ratiovalues for the signal intensities. The ratio values are plotted againstthe associated centroid values. The centroid values for the intensityratios can be determined using the equation (2) above. A calibrationfunction can also be obtained, for example, a linear regressionfunction. For example, a calibration function for the graph 1500 can beexpressed as y=mx+b; where “m” is the slope of the line and “b” is they-intercept. For a particular sample film, once the intensity ratio isdetermined as described above, the centroid value can be obtained fromthe linear equation as centroid=x=y−b)/m.

An other embodiment of the present invention pertain to a method toisolate the signal emitted by a first species (signal spectrum) from thesignals emitted by different species (background spectra) whose initialemission kinetic energy is larger than the kinetic energy of the firstspecies. The photoelectrons emitted by the different species will loseenergy through inelastic scattering and will be detected in the sameenergy range as the photoelectrons from the first species. The detectedspectrum is the sum of the background spectrum and the signal spectrum.One method to subtract the background spectrum from the measured spectrais to obtain an independent measurement of the background spectrum, i.e.by collecting a photoelectron spectra on a sample (background sample)with the same bulk/surface property of the sample of interest thatdoesn't contain the element to be analyzed.

Often it is difficult to prepare such a background sample. Oneembodiment of the present invention pertains to a method ofreconstructing the background spectrum from prime principles usingelectron transport theory. Most of the background elements of which thebulk is composed have known (or uniform depth distribution), therefore,given the intrinsic spectra for each of the species at high emissionkinetic energy the full background spectra can be reconstructed,normalized and subtracted to isolate the spectra of the photoelectronsemitted by the species with unknown depth distribution.

For instance, referring to FIG. 14, a film may include hafnium (Hf),silicon (Si), and nitrogen (N). In one case, nitrogen is the element ofinterest. In one example, for a total spectrum of the film, a peak atabout 1250 KE is that of Hf_(4f) from hafnium, another peak at about1050 KE is that of Si_(2p) from silicon, another peak at about 850 KE isthat of Si_(2s) from silicon, and at about 800 is an N1s from nitrogen.As illustrated here, the spectral lines (or spectra) from Hf_(4f) fromhafnium, and Si_(2p) and Si_(2s) from silicon contribute to thebackground of the spectral line (spectrum) for the nitrogen N_(1s).Thus, to analyze or isolate the signals form the N_(1s), region only,the spectra particular to Hf_(4f), Si_(2p), and Si_(2s) need to beremoved. In the absence of an appropriate reference film the backgroundspectral line(s) can be simulated using one or more exemplary methods ofthe present invention.

FIG. 15 illustrates an exemplary method 2200 which illustrate a methodof analyzing one or more elements in a film such as the film similar tothe film shown in FIG. 14. One or more elements in a film can be thebackground materials for another element in the film. In method 2200,one element's spectrum is obtained first and then used as the backgroundspectrum for another element. In one embodiment, the species thatexhibits the highest kinetic energy (KE) is analyzed first and used as abackground for the spectra associated with all the other lower emissionkinetic energy species. In the example shown in FIG. 14, the Hf_(4f)spectrum will be analyzed and reconstructed first. Being the highestemission kinetic energy species its background is just residualradiation that can be approximated with a linear fit. A subregion of thespectra containing solely the Hf_(4f) spectral region is selected andused to determine the Hf_(4f) depth distribution as described previouslyin the N1s example. The step of determining the Hf_(4f) spectrum depthdistribution can be skipped if it is known already—as in the case wherethe Hf_(4f) spectrum is part of the bulk uniform material. Given theHf_(4f) depth distribution a simulated spectrum can be generated overthe whole energy range collected in the measured spectrum and afterproper normalization subtracted. The subtracted spectrum now will be thesuperposition of the spectra of the remaining species, in this examplethe N1s, Si_(2p) and Si_(2s). The same process can be repeated for thenext highest emission kinetic energy species.

Alternatively the depth distribution of each of the species can be foundsimultaneously with optimization method similar to the one explained inthe N1s example by minimizing the difference between the full measuredspectrum and a simulated spectrum that is given by the superposition ofthe spectra simulated for each of the species. Since the full spectrumis analyzed, beginning from the highest emission kinetic energy species,there is no need to subtract the background spectra from species athigher emission kinetic energy.

In order to carry out the full spectral analysis it is required todetermine the intrinsic for each of the species present in the spectrumunder analysis. In order to do a set of reference wafers for which thedepth distribution of all species is known is needed. For example a bareSi wafer can be used to extract the Si metal intrinsic spectrum, a pureHfO2 wafer can be used to determine the Hf4f Hf 4d, Hf4p intrinsic andO2s, O1s and so on. . . . Referring to FIG. 16, for each referencewafer, at 701, the energy region containing solely the spectrum of thehighest emission kinetic energy line is selected. At 703, the intrinsicspectrum for that species is computed over that energy range andlinearly extrapolated to zero at the lower energy. At 705, the fullenergy range spectrum is generated using the intrinsic spectrum found at703 and the known depth distribution for that element. At 707, thereconstructed spectrum is subtracted from the measured spectra obtaininga background subtracted spectrum for the next species. The sameprocedure is repeated on the background subtracted spectrum for the nexthighest kinetic energy species.

The intrinsic spectra found analyzing the reference wafers with theembodiment described in FIG. 16 can be used to determine the unknowndepth distribution of one or more elements in the sample film aspreviously described. The process of generating a simulated spectrum orsimulated spectra in real time during regression can be time consuming.In order to overcome this difficulty one can pre-compute PI coefficientsfor each spectrum and use the PI coefficients to reconstruct thespectrum.

In one embodiment, a method is provided to simulate, in real time, amodeled spectrum with a known distribution profile. The PI coefficientscharacteristic of the depth distribution of a given species and thescattering process (elastic and inelastic) are pre-computed, forexample, using a Monte Carlo or other suitable methods. The PIcoefficients are pre-computed for a sparse set of depth distributionsand stored in a PI coefficients database. Such set of PI coefficientscan be organized in the database as a function of parameters definingthe associated depth distributions. During real time simulation of thespectrum associated to an arbitrary depth distribution the appropriatePI can be found by interpolating the pre-computed PI in the space ofparameters describing the depth distribution. The interpolated PIcoefficients are than used to reconstruct the spectrum to be used as asimulated spectrum (for example a background spectrum or a signalspectrum pertaining to the element of interest) or to reconstruct thescattering contribution to be subtracted from a processed spectrum (aspreviously discussed) to obtain an intrinsic spectrum. The same type ofinterpolation scheme can be done if the full spectra associated to thesparse set of depth distribution is stored, but that would require amuch larger storage memory for the database.

Embodiments of the present invention are particularly advantageous incharacterization of certain oxide layers. For example, such oxide layersmay include silicon oxide layers, oxynitride films, nitrided oxidelayers, silicon oxynitride (ONO) films, etc. For example, such oxidelayers may be formed as thin films having thicknesses less than about 10nanometers, and even 2 nanometers, and used for gate oxides in thefabrication of semiconductor devices such as field effect transistors(FET). Such transistors are used in various integrated circuit devicesincluding processing devices, memory devices, etc. Further, the presentinvention is advantageous in measuring the shape and dose of thinimplant regions with accurate quantitative results and chemicalcomposition information. For example, a silicon substrate may beimplanted with BF₂ in the formation of semiconductor devices. Thepresent invention may be used to characterize such a formed implantedthin layer or region by depth profiling the implanted silicon substratesample.

Additionally, embodiments of the present invention can be used inpredicting electrical performances or parameters of devices that areformed in or on the sample film as previously described. FIG. 17illustrates an exemplary process 5000 of using predicted electricalproduct performance using distribution profile, thickness, and/orcentroid value of an element in a sample film 5004. The sample film 5004may be formed on a substrate sample 5002 such as a wafer. Thedistribution profile, thickness, and centroid value of the element inthe sample film 5004 can be determined as previously described. In oneembodiment, the sample film 5004 is put through a profiling system 5006for the distribution profile, thickness, and centroid valuedetermination as previously described. The values obtained from theprofiling systems 5006 are then passed to a predict product performanceanalysis system 5008. Here, the distribution profile of the element,centroid value of the element, and the film thickness are then used topredict electrical parameters for devices that are to be formed in or onthe sample film. For instance, drive current and threshold voltage of adevice can be predicted using the centroid value for the element toyield “predicted electrical parameters.” The predicted electricalparameters can then be fed into a fabrication process controller 5010 sothat process parameters can be controlled, monitored, and/or modifiedaccordingly or according to desired product performance. For instance,the temperature, pressure, time, thickness, dose, etc. . . . for formingthe sample film can be monitored and/or modified to achieve a desirableresult using a centroid/thickness value. Additionally, a dimensionlessvalue such as centroid/thickness can be used to correlate to aparticular electrical parameter. Thus, an electrical parameter of a filmcan be predicted, monitored, controlled, or modified using the resultsobtained from the profiling system. The fabrication process controller5010 can use the information to control other processes (box 5012) in asystem, such as controller the deposition, implantation, or etchingprocesses that are used in device fabrication.

FIG. 18 illustrates an exemplary process 5001 of using predictedelectrical product performance using distribution profile, thickness,and/or centroid value of an element in a sample film 5004. As before,the sample film 5004 may be formed on a substrate sample 5002 such as awafer. The distribution profile, thickness, and centroid value of theelement in the sample film 5004 can be determined as previouslydescribed. In one embodiment, a photoelectron system such as an XPSsystem with an X-ray source 5006 is used to excite photoelectron(s) fromthe sample film 5004 for analysis are previously described. An analyzer5008 is used to analyze the sample film 5004 as previously described.The data are then put through a profiling system 6000 for analysis suchas distribution profile, thickness, and centroid value determination aspreviously described.

In the profiling system 6000, analysis such as intensity ratiosdetermination, distribution profile and centroid value determination areperformed as previously described. In one embodiment, signal intensitiesfor an element are obtained and an intensity ratio is generated. Theratio is correlated against a calibration function to determine acentroid value for the element as previously described. In anotherembodiment, a measured spectrum for an element is obtained. A backgroundsubtraction is performed using any one of the methods previouslydescribed to obtain a processed spectrum. Minimization and optimization(using appropriate parameters to simulate a simulated spectrum) are thenperformed to determine a distribution profile for the element usingmethods previously described. A centroid value can also be derived.

The values obtained from the profiling systems 6000 are then passed to apredict product correlation system 7000. Here, the values are correlatedto parameters such as temperature, time, pressure, thickness, andelectrical parameters. The distribution profile of the element, centroidvalue of the element, and the film thickness can be then used to predictelectrical parameters for devices that are to be formed in or on thesample film as previously discussed. For instance, drive current andthreshold voltage of a device can be predicted using the centroid valuefor the element to yield predicted electrical parameters. The predictedelectrical parameters can then be fed into a fabrication processcontroller 8000 so that process parameters can be controlled, monitored,and/or modified accordingly or according to desired product performance.For instance, the temperature, pressure, time, thickness, dose, etc. . .. for forming the sample film can be monitored and/or modified toachieve a desirable result using a centroid/thickness value.Additionally, a dimensionless value such as centroid/thickness can beused to correlate to a particular electrical parameter. Thus, anelectrical parameter of a film can be predicted, monitored, controlled,or modified using the results obtained from the profiling system. Thefabrication process controller 8000 can use the information to controlother processes (box 9000) in a system, such as controller thedeposition, implantation, or etching processes that are used in devicefabrication.

As one skilled in the art will recognize from the description above, thesample may take one of many different forms. For example, the sample maybe a layer formed on a substrate or a region formed within a substrate,as well as any other sample formed of a material that would benefit frombeing characterized according to the present invention. As such, thepresent invention is not to be taken as limited to any particularmaterial or structure listed herein. However, the present invention doeshave particular advantages in characterizing certain thin films, e.g.,gate dielectric layers such as gate oxide layers.

While the invention has been described in terms of several embodiments,those of ordinary skill in the art will recognize that the invention isnot limited to the embodiments described. The method and apparatus ofthe invention, but can be practiced with modification and alterationwithin the spirit and scope of the appended claims. The description isthus to be regarded as illustrative instead of limiting.

Having disclosed exemplary embodiments, modifications and variations maybe made to the disclosed embodiments while remaining within the spiritand scope of the invention as defined by the appended claims.

1. A method comprising: collecting a set of reference backgroundintensity spectra for a set of reference films as a function of aselected parameter surrounding said reference films, each of saidreference film constituting a bulk material for a sample film; removinga background intensity spectrum from a measured intensity spectrum forsaid sample film to generate a processed spectrum, wherein said samplefilm having an element of interest deposited therein, wherein saidbackground intensity spectrum to be removed is one of (a) a referencebackground intensity spectrum collected for said reference backgroundintensity spectra that has said selected parameter matching said samplefilm, and (b) an interpolated background intensity spectrum from saidset of reference background intensity spectra.
 2. The method of claim 1,wherein said selected parameter includes a film thickness and whereinsaid set of reference background intensity spectra is collected as afunction of film thickness, and wherein said background intensityspectrum to be removed is one of (a) a reference background intensityspectrum collected for said reference background intensity spectra thathas a film thickness matching a film thickness of said sample film, and(b) an interpolated background intensity spectrum from said set ofreference background intensity spectra using a film thickness for saidsample film.
 3. The method of claim 2, further comprising: optimizing asimulated intensity spectrum as a function of a simulated profiledistribution for said element in said sample film; matching saidprocessed spectrum to said simulated intensity spectrum using aminimization algorithm; and determining a distribution profile for saidelement in said sample film based on said optimizing and matching. 4.The method of claim 3, wherein said method is automated.
 5. The methodof claim 4, wherein said matching is includes automatically optimizingsaid simulated intensity spectrum as a function of simulateddistribution profile and matching said processed spectrum to saidsimulated intensity spectrum, and repeating said optimizing and matchinguntil a match or a close match is obtained.
 6. The method of claim 5,further comprising: determining a centroid value for said element insaid sample film; determining a dose level for said element in saidsample film; correcting a dose level for said element for said elementin said sample film; predicting an electrical parameter for a device tobe formed in or on said sample film; and controlling an electricalparameter for a device to be formed in or on said sample film.
 7. Themethod of claim 4, further comprising: determining a centroid value forsaid element in said sample film; determining a thickness of said samplefilm; obtaining a ratio of said centroid value and said thickness forsaid sample film; and performing one of monitoring, predicting, andcontrolling one or more electrical parameters for one or more devices tobe formed in or formed on said sample film.
 8. The method of claim 1,wherein said set of reference background intensity spectra is collectedusing a photoelectron spectroscopy system taking measurements for saidset of reference films at a constant emission angle, and wherein saidmeasured intensity spectrum is collected using said photoelectronspectroscopy system taking measurements for said sample film at saidconstant emission angle.
 9. The method of claim 1, wherein optimizingthe simulated spectrum as a function of element distribution profile andmatching said processed spectrum to said simulated spectrum furthercomprises defining one or more parameters used to generate the simulatedspectrum.
 10. The method of claim 9, wherein said one or more parametersare chosen based on a Signal-to-Noise analysis.
 11. The method of claim10, wherein optimizing the simulated spectrum as a function of elementdistribution profile and matching said processed spectrum to saidsimulated spectrum further comprises minimizing pre-computed figure ofmerit for the simulated spectrum and determining minimization byinterpolation from a figure of merit surface.
 12. A method comprising:obtaining a intensity spectrum for an element in a sample film using aphotoelectron spectroscopy system and using a constant emission angle;determining a centroid value for said element in said sample film usingsaid intensity spectrum, wherein said method is non-destructive to saidsample film; correlating said centroid value to one or more electricalparameters for said sample film; and performing at least one ofmonitoring one or more fabrication process for said sample film,controlling one or more electrical parameters for said sample film,engineering one or more fabrication process for said sample film,predicting one or more fabrication process for said sample film, anddetermining and correcting a dose for said element based on saiddetermined centroid value.
 13. A method comprising: obtaining a measuredspectrum for a film having signals emitted by a plurality of species,each species having an emission kinetic energy, said measured spectrumcovering a plurality of subregions; obtaining an intrinsic function fora first species which has the highest emission kinetic energy at a firstpredetermined subregion; and reconstructing a complete first spectrumfor said first species having the highest emission kinetic energy, saidcomplete first spectrum covers all subregions of said measured spectrum,and reconstructing is accomplished using said intrinsic function and anextrapolation method.
 14. The method of claim 13, further comprising:using the complete first spectrum as a background spectrum to a secondspecies which has the second highest emission kinetic energy.
 15. Themethod of claim 13, further comprising: subtracting said backgroundspectrum from said measured spectrum; and obtaining a second intrinsicfunction for said second species at a second predetermined subregion;and reconstructing a complete second spectrum for said second specieshaving the second highest emission kinetic energy, said complete secondspectrum covers all subregions of said measured spectrum, andreconstructing is accomplished using said second intrinsic function andsaid extrapolation method.
 16. The method of claim 15, furthercomprising: optimizing a simulated intensity spectrum as a function of asimulated profile distribution for a first element associated with saidfirst species in said film; matching said complete first spectrum tosaid simulated intensity spectrum using a minimization algorithm; anddetermining a distribution profile for said first element in said filmbased on said optimizing and matching.
 17. The method of claim 16,further comprising: determining a centroid value for said first elementin said film; determining a dose level for said first element in saidfilm; correcting a dose level for said element for said first element insaid film; predicting an electrical parameter for a device to be formedin or on said sample film; and controlling an electrical parameter for adevice to be formed in or on said film.
 18. The method of claim 15,further comprising: optimizing a simulated intensity spectrum as afunction of a simulated profile distribution for a second elementassociated with said second species in said film; matching said completesecond spectrum to said simulated intensity spectrum using aminimization algorithm; and determining a distribution profile for saidsecond element in said film based on said optimizing and matching. 19.The method of claim 18, further comprising: determining a centroid valuefor said second element in said film; determining a dose level for saidsecond element in said film; correcting a dose level for said elementfor said second element in said film; and controlling an electricalparameter for a device to be formed in or on said film.
 20. The methodof claim 13, wherein said measured spectrum is collected using aphotoelectron spectroscopy system taking measurements for said film at aconstant emission angle.
 21. A method comprising: computing a set ofstatistical coefficients characteristic of a set of spectra, said set ofstatistical coefficients organized in a database as a function ofselected parameters that define a reference film; simulating abackground spectrum for a sample film using said database and a knownparameter for said sample film; and subtracting said background spectrumfrom a measured spectrum for said sample film to generate a processedspectrum for said sample film.
 22. The method of claim 21, furthercomprising: optimizing a simulated intensity spectrum as a function of asimulated profile distribution for an element in said sample film;matching said processed spectrum to said simulated intensity spectrumusing a minimization algorithm; and determining a distribution profilefor said element in said film based on said optimizing and matching. 23.The method of claim 22, further comprising: determining a centroid valuefor said element in said sample film; determining a dose level for saidelement in said sample film; correcting a dose level for said elementfor said element in said sample film; and controlling an electricalparameter for a device to be formed in or on said sample film.
 24. Themethod of claim 21, wherein simulating said background spectrum for saidsample film further comprising: determining whether said known parameterof said sample film matches one of said selected parameters for saidstatistical coefficients computed from said spectra; selecting one ormore appropriate statistical coefficients associated with said knownparameter when said known parameter matches one of said selectedparameters or interpolating from said selected parameters to compute oneor more appropriate statistical coefficients for said known parameter;and using said appropriate statistical coefficients to simulate saidbackground spectrum.
 25. A method comprising: simulating a backgroundspectrum for a film using a set of first partial intensity coefficientsobtained for at least one bulk element expected to be present in saidfilm, said film further comprising an element of interest; and whereinsaid first partial intensity coefficients are computed from at least onereference film having said at least one bulk element and wherein anenergy spectrum for said at least one reference film is used for acomputation of said first partial intensity coefficients.
 26. The methodof claim 25 further comprising: collecting a set of spectra for a knownset of parameters; and computing second partial intensity coefficientsfor said set of spectra using a Monte Carlo (MC) simulation; whereinsaid set of parameters comprise sufficient sampling points to allow foran interpolation from said second partial intensity coefficients. 27.The method of claim 26 further comprising: interpolating said firstpartial intensity coefficients for said film using said second partialintensity coefficients; and reconstructing a spectral line frominterpolated first partial intensity coefficients to simulate saidbackground spectrum.
 28. The method of claim 27 further comprising:removing said background spectrum from a film spectrum obtained for saidfilm to obtain a processed spectrum.
 29. The method of claim 28 whereinsaid set of parameters include at least film thickness.
 30. The methodof claim 29 further comprising: performing an minimization andoptimization on said processed spectrum with said at least one simulatedspectrum for said matching.
 31. The method of claim 30 furthercomprising; determining at least one of a distribution profile, acentroid value, and a dose for said element of interest in said film.32. A method of storing spectral data comprising: collecting at leastone spectrum for a film having at least one element; computing one ormore partial intensities coefficients for said at least one spectrum;and storing said one or more partial intensities coefficients;
 33. Themethod of claim 32 wherein said at least one spectrum is collected usingan XPS system.
 34. The method of claim 32 wherein said computing is doneusing a Monte-Carlo simulation.
 35. The method of claim 32 wherein anexecutable program with instructions is provided to use computed partialintensity coefficients to reconstruct said at least one spectrum.
 36. Amethod comprising: collecting electron spectra for a film at variouscollection angles to generate collected spectra; eliminating surfacescattering contribution from the collected spectra using a deconvolutiontechnique to subtract one or more systematic errors due to interfacecrossing; performing minimization on said collected spectra bysimulating a set of simulated spectra that account for elasticscattering, and minimizing said set of simulated spectra with saidcollected spectra; and determining a distribution profile for an elementin said film.
 37. The method of claim 36 wherein the set of simulatedspectra is generated as a function of distribution profile for saidelement in said film.
 38. The method of claim 37, further comprising atleast one of: determining a centroid value for said element in saidfilm; determining a dose level for said element in said film; correctinga dose level for said element in said film; predicting an electricalparameter for a device to be formed in or on said film; and controllingan electrical parameter for a device to be formed in or on said film.39. A method comprising: obtaining a first spectrum associated with anelectron energy excited from one or more elements in a sample film;obtaining a processed spectrum by at least preprocessing the firstspectrum to eliminate angle dependent surface scattering contributions;and matching said processed spectrum to a simulated spectrum as afunction of element distribution profile.
 40. The method of claim 39wherein an x-ray photoelectron spectrometry (XPS) or an angular resolvedx-ray photoelectron spectrometry (ARXPS) is used to obtain said firstspectrum.
 41. The method of claim 39 further comprises at least one of:determining a distribution profile for said one or more elements in saidsample film based on the matching and minimizing. determining a centroidvalue for said one or more elements in said sample film; determining adose level for said one or more elements in said sample film; correctinga dose level for said element for said on or more elements in saidsample film; predicting an electrical parameter for a device to beformed in or on said sample film; and controlling an electricalparameter for a device to be formed in or on said sample film.